1. Field of the Invention
The present invention relates to a manufacturing method of a solid oxide fuel cell (sintered body), and a manufacturing method of a compact of a divided member of the cell. In the present specification, the “compact” means the state before the sintering.
2. Description of the Related Art
There has conventionally been known a cell (single cell) of a solid oxide fuel cell (SOFC) including a fuel-side electrode, a solid electrolyte, and an oxygen-side electrode, which are successively stacked on a plate-like support member (conductive member) having a fuel channel formed therein (see, for example, Japanese Unexamined Patent Application No. 2007-95383). A fuel gas (hydrogen gas, etc.) is supplied to the fuel channel in the support member, and a gas (air, etc.) containing oxygen is supplied to the oxygen-side electrode, whereby a potential difference is produced between the fuel-side electrode and the oxygen-side electrode based upon a difference in concentration of oxygen ion in the solid electrolyte.
Japanese Unexamined Patent Application No. 2007-95383 described above discloses a manufacturing method of the SOFC cell as described below. Specifically, a compact of a support-member divided-member, which is obtained by dividing a plate-like support member having a fuel channel formed therein into two (so as to divide the fuel channel into two in the thickness direction), is manufactured by a press molding. A channel pattern corresponding to the fuel channel is formed on the lower surface of the compact of the support-member divided-member. In the press molding, powder of a raw material of the support member is injected into a molding die having the pattern corresponding to the channel pattern formed on a molding surface at the bottom wall, and the powder of the raw material is pressed by a press molding machine with a predetermined pressure.
Next, two compacts of the support-member divided-member, which are manufactured as described above and taken out of the molding die, are prepared. The two compacts of the support-member divided-member are bonded to each other with a predetermined bonding agent in such a manner that the surfaces having the channel pattern formed thereon are agreed with each other, whereby a bonded compact of the support member is formed.
Then, a compact of a fuel-side electrode, and a compact of a solid electrolyte are successively formed on the bonded compact, whereby a stacked compact is formed. The stacked compact is sintered, so that a stacked sintered body is formed. Next, a compact of an oxygen-side electrode is formed on the solid electrolyte of the stacked sintered body. Then, the compact of the oxygen-side electrode is sintered, whereby an SOFC cell in which “the fuel-side electrode, the solid electrolyte, and the oxygen-side electrode are successively stacked on the plate-like support member having the fuel channel formed therein” is formed.
The reason why the method of bonding two compacts of the support-member divided-member manufactured by the press molding is employed to manufacture the compact of the support member having the fuel channel formed therein by the press molding is because the degree of freedom in the shape of the fuel channel is increased, and hence, the fuel channel having the complicated shape can easily be formed.
In the method described in Japanese Unexamined Patent Application No. 2007-95383, the compact of the support-member divided-member is formed by the press molding of the powder of the raw material. In general, in the press molding, a fine powder of the raw material (primary particle) is processed beforehand into a relatively coarse group (granular body, secondary particle) with the use of a spray drying method in order to facilitate the press molding, and the secondary particle is pressed to form the press-molded body. Specifically, the press-molded body is composed of the secondary particles. Therefore, the support member (sintered body) formed by sintering the press-molded body is also composed of the secondary particles, so that the diameter of the secondary particle constituting the support member (sintered body) is relatively large such as about 80 μm. Because of this, the number of contacts at the interface between the support member (the sintered body of the press-molded body) and the fuel-side electrode is reduced, whereby it is difficult to secure the sufficient contact area at the interface. Therefore, a satisfactory electrical connection between both of them is difficult to be secured. As a result, the electric resistance (ohmic resistance) as the whole SOFC cell is relatively increased, which might entail a problem that the output density of the whole SOFC tends to be relatively low.
Further, in the method described in Japanese Unexamined Patent Application No. 2007-95383, the compact of the fuel-side electrode and the compact of the solid electrolyte are successively formed on the bonded compact of the support member, which is formed by bonding two compacts of the support-member divided-member taken out of the molding die to each other. When the respective compacts are formed on the bonded compact of the support member, the respective compacts are generally pressed from above in the thickness direction in order to prevent the peeling of the respective compacts. However, the bonded compact of the support member has not yet been sintered, so that it is relatively easy to be warped when it receives external force, and it may be damaged due to a crack. In particular, the fuel channel (cavity) is formed in the bonded compact of the support member. Therefore, the warpage is easy to be caused on the portion in the vicinity of the region of the bonded compact where the fuel channel is formed when it receives the contraction force in the thickness direction, resulting in that it may be damaged due to a crack. Accordingly, in the press molding, the degree of freedom in designing the shape of the fuel channel is restricted, and it is difficult to enhance the output density of the cell.